This invention relates to laminated footwear insulation material.
In outdoor recreational footwear, proper insulation is particularly important. Such insulation should have the properties of low thermal conductivity, breathability and moisture resistance. In addition to these properties, footwear insulation material should also be characterized by a wide range of mechanical properties, such as tensile strength, elasticity, cold temperature flexibility and abrasion resistance.
Several insulation materials in use today exhibit, some of these properties but often such materials are only effective in compositions too heavy or too bulky for practical footwear application. Insulation materials which may have the desired lightweight composition or thinness do not possess the required insulating properties.
Thus, there is a need for an extremely thin effective insulating material having superior thermal insulation and moisture vapor transmission characteristics; and also exhibiting the necessary mechanical properties.
The present invention is directed to an insulation composition and method of producing the same. Broadly the invention comprises a urethane membrane secured to a foam layer by an adhesive system. A plurality of needle punched fibers are secured to the membrane and extend through and beyond the foam layer. The material has a thermal insulation factor R of between about R18.0 to R19.0 based on ASTM C-177-76 and is substantially liquid impermeable--gas and moisture vapor permeable. The moisture vapor transmission factor measured according to PSTC-34(11/70) ranges between 0.35 to 0.65.
More particularly, the composition comprises a polyurethane membrane which is adhesively joined to a polyurethane foam. The foam has a density of 1.0 to 2.3 pounds per cubic foot, say for example 1.5 to 1.8 pounds per cubic foot. The foam and membrane are needle punched with polymeric fibers of between 2 to 6 denier, say for example 4 denier and between about 600 to 1400 punches per square inch, say preferably between 800 to 1000 punches per square inch, for example between 860-900 punches per square inch. The composition is impermeable to liquids but is gas and vapor permeable. The present invention embodies an extremely thin laminated insulating material wherein the foam is between 0.030-0.090 inch, say for example 0.050-0.70 inch, preferably 0.060 inch gauge, and the membrane to which it is adhered is between 0.0008-0.0012 inch, preferably 0.001 inch.
The superior thermal insulating properties of the composition are complemented by superior mechanical properties. The composition has tensile strength of 3000 psi at 500% elongation, excellent humid aging 160.degree. F. at one week (80%-95% R.H.) and cold temperature flexibility at -65.degree. F. FED-STD-191, Method 5874. The composition has an elongation of approximately 800% before breaking ASTM D2370. In the preferred embodiment, a layer of polyurethane foam, either open cell or closed cell, is joined to a cast urethane membrane by an adhesive system. A plurality of polypropylene fibers are needle punched into the membrane and pass through and extend beyond the foam layer.
Other additives may be incorporated into the composition to provide antifungal and antibacterial characteristics.